Mercedes boss Toto Wolff says he expects a close race between Lewis Hamilton and Nico Rosberg in the Malaysian Grand Prix despite the defending champion enjoying a renewed swing in fortunes at Sepang.

Arriving in Malaysia on the back of a lacklustre run to third position in the Singapore Grand Prix, a result that saw him cede his championship lead to dominant race winner Rosberg, Hamilton has nonetheless largely dominated at Sepang this weekend thus far.

With Hamilton qualifying on pole position by almost half-a-second - two weeks after Rosberg put 0.7s between them in Singapore -, Wolff admits the constant shifts in momentum between the two Mercedes drivers is difficult to explain.

"It's quite surprising and when you hear them talking about why that is... they just don't feel as comfortable as the other driver in the car," he said. "Whether that is down to specific set up issues, Lewis was handicapped by the lack of running in Singapore. As big as those gaps might seem today, these two just keep pushing each other constantly. If one is on the back foot, suddenly we see such a big gap.

Despite this, Wolff expects the race itself to be something of a tighter affair between the two drivers in what he doesn't think will be a 'flat out' race.

"I think [the race is] open because the pace on the long runs was not as different. We know with the current generation of the cars and the heat, tomorrow is going to be an exercise of how you make the car, the systems, the tyres, the engine and everything survive best. So I don't think it will be flat-out for one-and-a-half hours. Everything is possible. The start plays a big role.

Even so, Wolff says he hopes the much speculated 'Rules of Engagement' will apply to the drivers without prompt to ensure a strong result for title sponsor Petronas on home soil.

"The more we come to the end of these season and as close as it is between the two of them, there is a lot at stake. In Malaysia, where we haven't been able to win the race last year, means we could secure the constructors trophy for Petronas and the Malaysian fans would be great.

"Do we need to remember? They have had the odd moment but they know exactly about the effort in the background and obviously bringing it home in Malaysia would mean a lot to the team and Petronas and them. We have spent a week here doing activation. They know it's very important."